A Biostatistics Core (BC) is being developed to provide a series of functions that are central to the goals of the Berkeley/Stanford Children's Environment Health (Pre)-Center (CHP-C). Two of the functions can be considered generic to any research center and one is unique to the CHP-C. The two generic functions are: 1) to work in collaboration with the data management team to assure the quality of the data that are used for all analyses by all investigators; and 2) to provide statistical input required for all data analyses being carried out by all investigators. The unique goal is to continue the work that has been done by the PI and his statistical collaborators in the application of causal statistical methods (CSMs)various applications of marginal structural models (MSMs) to environmental health research. As will be explained below, this latter collaboration involves the application of evolving methods to estimate causal parameters and the development of user-friendly and computationally efficient software. Application of causal statistical methods has facilitated analyses that heretofore were not addressed appropriately by more